Testing insulation



Jan. .21', l1947.

c. M. Ross TESTING INSULATION fmed oct. 18. 1944 INVETUR BYA ATTORNEYPatented Jan. 21, 1947 UNITED STATES PATENT OFFICE TESTING INSULATIONApplication October 18, 1944, Serial No. 559,143

7 Claims.

This invention relates to testing apparatus and methods, andparticularly to apparatus and methods for testing insulation inconnection with cables, drop wires leading from a line to a subscriberspremises, or insulation occurring elsewhere in the telephone plant,

The testing set of the present invention is particularly adapted tomeasure the line insulation of subscribers lines during and after wetweather. If, due to poor insulation, the leakage to ground or from onewire to the other is greater than an allowable value, an indication ofthis fact will be given by the set. Preferablylthe set is designed sothat it will make tests of tip-to-ground leakage, ring-to-groundleakage, and tip-to-ring leakage, If any one of these leakages exceedsan allowable value, the fact may be noted and steps taken to locate thecause of the defect and correct it.

Another feature of the test set of the present invention is that foreach line it will automatically make the three tests above mentioned inregular successive order without any circuit manipulated by theoperator. All the operator has to do is to note certain signals intesting a given line, and record their meaning. The beginning and end ofthe test is indicated either visually r audibly, or both, and after agiven line is tested the operator shifts the contact shoe used to makecontact with the line to the next line to be tested.

Preferably the test set of the invention performs the followingfunctions:

(a) It provides visual or audible signals, or both, if the line to whichit is connected is busy.

(b) If the line tests busy, the circuit of the set is sc arranged thatit will not cause interference with the busy line.

(c) While testing an idle line, the set renders the line busy to allcalls.

(d) It makes accurately timed and uniform tests of the leakage to groundfrom each side oi the line, and of the leakage between wires.

(e) It produces visual or audible signals, or both, if the insulationresistance of the line is 'below limits determined by the voltage usedin making the test.

(f) If no trouble is encountered after it has completed its cycle oi?`tests for a given line, it stops further testing until the contact shoeis moved to the next line; and if a defect is indicated by any one ofthe tests, it locks up on that test and does not make other tests forthat line.

Operation of the set does not require any detailed knowledge of the testset or of the subscribers line circuit. Consequently the testingoperations may be performed by nontechnical and relatively unskilledpersonnel.

The invention may be more fully understood from the followingdescription when read. in connection with the accompanying drawing, thesingle ligure of which illustrates a preferred form of the invention.

GENERAL DESCRIPTION OF TESTING APPARATUS The test set is provided with acontact shoe in` dicated by the dotted line rectangle SH in the lowerright-hand corner of the drawing. This contact shoe is provided withthree contacts, s, 1* and t, which make contact respectively with thesleeve, ring and tip terminals of successive lines to be tested as theoperator moves the shoe manually along the terminal block of a,distributing frame.

Two relays BY and ST are associated with the sleeve contacts of theshoe. Relay BY operates when a busy line is encountered, and to causethe pass-by lamp BYL to glow, and to operate abuzzer BZR. The relay BYalso disconnects ground from other parts of the set to preventinterference with the busy line by the test set.

If the line is not busy the relay ST operates and remains operated untilthe series of tests have been completed. The operation of the relay STinstitutes a series of three tests: (a) a test of the leakage resistancebetween the tip conductor of the line and ground; (b) a test of theleakage resistance between the ring and ground; and (c) a test of theleakage resistance between the two wires of the line.

A slow operating relay SR is controlled-by the relay ST, and isenergized four successive times in making a complete cycle of tests. Therst time the relay SR is energized and then released it conditions thecircuit to make the tip-toground test. During this test it isre-operated and if a fault is detected by the test it is locked up to`stop further testing of the faulty line. If no fault is discovered itisreleased to start the ring-to-ground test. It is operated for the thirdtime during this test and is released to initiate the nal tip-to-ringtest if no fault is discovered on the second test. During the final testit is operated for the fourth time and locks up the circuit regardlessof whether or not the third test dis-` closes a, fault.

The relay SR controls two switching relays S01 and SO2, each of which isslow to operate and slow to release. It is through these relays, whichconf` trol corresponding test relays T1 and T2, thatI the relay SRsuccessively conditions the testing cir- 3 cuit to make thetip-to-ground, ring-to-ground and tip-to-ring tests above referred to.The circuit is so arranged that when the test relay T1 is operated alonea tip-to-gro-und test is made, and when the relay T2 alone is operated aringlays are operated simultaneously, 'a tip-to-ring test is made. Thetiming of all of these tests is the same and is determined by theoperating time required for the various relays, as will appear morefully hereinafter.

A common test relay T3 is provided and has associated therewith a testbattery whose voltage is determined in accordance withthe requirementsof the tests to be made. This relay Ta and test battery are connectedbetween the tip and ground for the rst test, between the ring and groundfor the second test, and between the tip and ring for the third test. Ifthe leakage resistance is above the minimum allowable on a given test,the relay Ts will not operate, and the relay SR will function to causethe circuit to be conditioned for Vthe succeeding test. This willcontinue until all three tests have been completed.

If,` on any one of the tests the leakage resistance is below theallowable minimum, the relay Ta will operate and cause the'ground lampGND to glow in the case of a tipto-ground or ring-to-ground test. In thecase of a tip-toring test, itwill cause the shunt lamp SHT to glow. Ineach case, the buzzerBZR, if provided, is actuated. At the same time thecircuit is locked up to prevent further tests and a lamp TST is causedto glow. WhenV this lamp glows simultaneously withV the ground lamp orthe shunt lamp, 'the operator will be informed that a defectivecondition has been found. The lamp TST is also arranged so that it willglow at the beginning of the test togindicate when each test isinitiated. When all three tests have been completed thelamp TSTglowsagain to indicate that fact. V'

As already stated the testing circuit is locked up and no furtherrtestsare made, if in testing a given line any one of the three tests shows adefect.` This simplies the operation and makes itunnecessary for theattendant to perform further operations in order to continue the tests.It is unnecessary to make further tests when a given test shows up adefective condition. This is becausedetermination of the fact that onedefect exists makes it necessary 'to send a maintenance man out to checkthe insulation of the line, and where defective, repair it. Properrepair of the line of course eliminates any other insulation faults thatmay exist.

OPERATION oF TEsT CIRCUIT WHEN LINE To BE 'TESTED Is BUSY Furtherdetails of the apparatus will be understood vin connection with adescription Vof the operation, which is as follows: As the attendantmoves the shoe SH along the terminal block of the distributing frame,the terminals s, r and t of the block make Contact with the sleeve, ringand tip terminals of a line. If the line is busy, the sleeve terminal ofthe line will be grounded. If `Vthe line is not busy, a differentcondition will exist. y For example, its sleeve conductor may haveapplied thereto yvoltage from a iS-volt battery through a 'cut-ofirelay. It will be noted that the windings ofthe relays BY and STarenormally connected in series in circuit Awith a 24,-volt battery. lTheserelays are so designed -to-ground test is made. When, however, both rethat neither relay will be operated when both are in series with eachother and with the 2li-volt battery. However, if the sleeve contact s isgrounded, as is the case where a tested line is busy, the circuit fromthe 2li-volt battery through the winding of the relay BY direct toground has lower resistance than when the relays BY and ST are in seriesin thev same circuit. Consequently the relay BY is operated.

On being operated, the pass-by relay BY opens its contact 2 anddisconnects ground from the armature of the start relay ST` to preventany of the other relays of the circuit from being operated. Thisprecludes any accidental connection between the tip or ring conductor ofthe line and any of the internal wiring of the set. At its contact l,relay BY connects ground to a circuit passing through the pass-by lampBYL and through the relay BZ to battery. The lamp BYL glows and therelay BZ causes the buzzer BZR to operate to apprize the operator thatthe line is busy, and the test shoe should .be moved on to the nextline.

OPERATION 0F TEsT vCIRCUIT WHEN LINE To BE TESTED Is IDLE (a.) Testingleakage from tip of Zine to ground If the test shoe SH encounters anidle line the Liii-volt battery connected to the sleeve conductor s ofthe line opposes the smaller current normally flowing through the relayBY and prevents false operation of that relay. At the same time thebattery on the sleeve increases the flow of current through the windingof the start relay ST to ground. The relay ST is thereforev operated andremains operated so long as'the sleeve conductor s remainsV in Contactwith the sleeve of the idle line. By connecting the shoe to an idle linethe ground through the winding of the relay ST of the test circuit isconnected over the sleeve contact s to the sleeve conductol` of the`line being tested. This ground makes the line under test appear busy toall other calls.

The relay SIluponbeing operated, closes the circuit at its contact lfrom ground over contact 2 of relay BY, contact i of relay ST, contactsI 2 of relay SO2, contacts I 2 of relay S01, and through the winding ofslow release relay SR, to battery. Relay SR now operates and at itscontacts 2 3 completes a circuit to operate *the relay S01 and to causethe test lamp TST to glow. This circuit extends from ground over Contact2 of relay BY, contact l of relay ST, over conductor x, over contacts 23 of relay SR to terminal ll and thence in parallel through the lamp TSTto grounded battery, and over contacts 8in-lb of relay T1 through thewinding of relay S01, to battery. The glowing of the lamp TST at thistime informs the operator that the line is not busy vand that the testsof the line are aboutrto proceed. l 1

The relay :S01 is slow to operate, but after a brief interval it pullsup its armature and opens its contacts I Z, thereby opening the circuitof the relay SR. At its contacts 3 4, relay S01 prepares a circuit tooperate the relay T1 in the manner which will appear presently.

The relay SR being slow to release, does not permit its armature to fall01T immediately, but after la brief interval it opens its contacts 2 3and closes its `contacts 2 I. Upon opening its contacts 2 3, the lampTST ceases to glow, and the circuit through the winding of the relay S01is broken. The relay S01 does not fall off immediately, however, as itis slow toY release.

When the relay SR opens its contacts 2 3, it al-so closes its contacts 2I. Relay S01, however, has not yet released its armature, and therefore,for an interval determined by the slowness of the relay S01 to release,the contacts 3 4 of said relay are closed concurrently with contacts 2 Iof relay SR. During this interval a circuit to operate the test relay T1is completed from battery through the lower winding of said relay, overcontacts #3 3 of relay S01, contacts I 2 of relay SR, over conductor x,and over contact I of relay ST and contact 2 of relay BY to ground. Thiscircuit remains closed until relay S01 releases.

In the meantime, relay T1 operates and closes 2, locking circuit frombattery through its upper winding, over its contacts It 2t, overconductor y, over contacts It 2t of deenergized relay T2, and thenceover contact I of relay ST and contact 2 of relay BY to ground. RelayT1, by opening its contacts Bln-'Ib and closing its contacts Sli-Gb,shifts the operating connection controlled by the relay SR from therelay S01 to the relay S02. The latter relay, however, is not operatedat this time, as the circuit is opened at contacts 2 3 of the relay SR.

Relay T1, by closing its contacts ih b, completes a test circuit fromthe tip conductor of the line under test, over contact t of the testshoe SH, over the tip conductor t of the test set, through a 100G-ohmresistance, over contacts b b of relay T1, over conductor m, overcontracts ih b of relay T2, through the upper winding of test relay T3,through the test battery B,

through the second winding of relay Ts, and over contacts 21a- Ib ofrelay T2 to ground.

When thi-stest circuit is completed, two conditions may occur: (a) Theresistance leakage to ground from the tip conductor of the line beingtested may be below normal, therebyindicating a defect, or (b) saidleakage resistance may be above the minimum limit, indicating a normalcondition. Assuming first that the leakage resistance is below normal,the current flow through the windings of the relay T3 will be largeenough to cause the operation of said relay. Relay T3, by closing itscontacts 9 5, completes a circuit from ground over said contacts, overcontacts St-t-Et of relay T2, over conductor o, through the ground lampGND, and through the winding of the relay BZ to battery. The ground lampGND therefore glows and the relay BZ causes the buzzer BZR to operate toapprize the person conducting the test that a defective condition hasbeen encountered. Relay T3, by closing its contacts B fl, also completesanother circuit from ground over said contacts, normal contact-s tt-6rof relay T2, over conductor p, closed contacts 'It-'t' of relay T1, andthrough the winding of the relay L0 to battery.

The operation of the relay L0 locks up the circuit and stops furthertests in the following manner: It will be recalled that relay SRreleased its armature and operated the relay T1 over the contacts 3 4 ofthe relay S01 and that relay T1 in turn opened the circuit of the relayS01. Upon having its circuit opened relay S01, after 2, slight delay,releases its armature. `At its contacts I 2 relay S01 again completesthe circuit of the relay SR, which is once more energized. Relay SR,upon re-operation, locks up over its contacts 4 5 and over the contacts3 2 of the now operated relay LO. Relay SR therefore remains locked upand operated until the circuit is restored by shifting the contact s of6 the shoe from the sleeve terminal of the line being tested.

Relay SR, upon being energized and locked up, closes a circuit over itscontacts 2 3 to operate the lamp TST and the relay S02. The circuit ofthe latter was prepared by the operation of the relay T1, which closedits contacts 8b 5b and opened its normal contacts 8b 'Ib, thussubstituting the connection to the relay SO2 for the previous connectionto the relay S01 as already described. The circuit for operating thelamp TST and the relay SO2 extends from ground over contact 2 of relayBY, over contact I of relay ST, over conductor over contacts 2 3 ofrelay SR to point I0, from which point the circuit proceeds in parallelthrough the lamp TST to battery, and over contacts 8b 5b and through theWinding of the relay S02 to battery. The operation of the relay S02 hasno significance at this time, but the lamp TST now glows in unison withthe previously4 operated ground lamp GND to apprize the operator that afaulty condition in the insulation has been found upon the tip-to-groundtest of the line.

The circuit remains locked up in this condition until the operator,after having recorded the fault in his log, moves the shoe to the nextline, thereby breaking the operating connection for the relay ST at thesleeve contact s of the shoe, and at the same time breaking theconnection of the test relay Ts at the tip contact t of the shoe. RelayST in falling off opens at its contact I the operating circuit of therelay SR. Relay T3 in opening its contacts 4 9, opens the circuitof therelay LO, which in turn opens the locking circuit of the relay SR. RelayT2, by opening its contacts A S, also opens the circuit of the groundlamp GND and the buzzer relay BZ. Relay SR falls off after its operatingand locking circuits have been opened, and thereby opens the circuit ofrelay S02 and the test lamp TST. The relay T1 is also released becauseits locking circuit passes over the contacts I 2 of the relay ST whichhas just been released.

(b) Testing leakage from ring conductor of line f to ground Assumingthat on the tip-to-ground testthe relay T3 was not operated because theleakage resistance indicated by that test was above the requiredminimum, the relay L0 would not have been operated and hence no lockingcircuit would have been provided for the relay SR when it was reoperatedas above described upon the release of the relay S01. The relay SR uponbeing reenergized, by closing its contacts 2 3, completes the circuitpreviously traced to operate the relay S02 and cause the lamp TST toglow,

This circuit, it will be remembered, passed over the closed contacts 8b6b of locked up relay T1. Due to the fact that the relay SR is notlocked up under the conditions above described, it releases its armatureafter a brief interval, and opens the circuit of the lamp TST and of therelay S02, thus extinguishing the lamp, The relay SO2, however, beingslow to release, does not immediately fall off. During the briefinterval after the relay SR has released and while the relay S02 isstill holding up its armature, a circuit is closed to operate relay T2from ground over contact 2 of 1 relay BY, contact I of relay ST, overconductor .'r, over contacts 2 I of relay SR, over contacts 4 5 of relayS02, and through the lower Winding of relay T2 to battery.

Relay T2, upon being energized, opens its con- 7 tacts ylt-2t andthereby breaks thev locking circuit of the relay T1, which is atonce-released. Relay T2,fby closing its contacts-3t 2t;-locks up throughits upper windingeto ground'over contact I ofi-relay ST and ,contactZ-of relay BY.

Relay T2 at `its contacts 2b 3b completes a ring-to-.ground'test circuitfrom the ring contact r'of the test shoe, over -conductor r' through a100G-ohm resistance, over' f contacts 3b 2b of locked up relay T2,through the middle Winding of relay Ta. throughbattery B, throughtheupper winding of relay T3, over contacts '5b-6b of relay T2, overconductor n, andv toground over vcontacts 2b lb of relay,T1,-i 1vhich`it will be recalled is at this time released.

As in the case of the tip-,to-ground test, the result of thisring-to-ground test Will depend upon whether the leakage resistance ofthe line is greater than or less than the minimum allow able Value. Letus assume rst that it is less than the allowable value,` as will be thecase when the insulation condition of the ringyconductor of the lineisvabnormal due to moisture entering cracks, or other defects of theinsulation.

Under -these conditions lthe relay T3 operates andestablishes aconnection from ground over its contacts `9 4, overcontacts 8t-9t ofrelay T2, over :conductor w, and thence over contacts 4t-3t of.relayT1,.-through the ground lamp GND and thetwindingof the `buzzer relay BZ,to battery. The ground lamp and the buzzer BZR are thereby actuated.- Atthe sametime the circuit for the rela-yLO is closed'irom. ground overcontacts 9 4 of relay-T3,:overcontactsBt-St of relay T2, over conductorw,v over contacts 4t 6t of relay T1, throughV the .winding of the relayVLO to battery. RelayLOtherefore provides a locking circuit over itscontacts 2 3 for the relay SR when it is operatedfor the third time.

This occurs as a resultoflthe Arelay T2 vbeing operatedfas abovedescribed. Relay T2 upon beingaoperated V`opens at its contacts 2t |t,the locking-.circuit of the relay T1. Relay T1 in turn, by opening itscontactsl 8b 6b, opensthe circuit of the relay SO2 and prepares a pathover contacts -8b' 7b for the relay S01.l When the relay SO2 releasesafter its circuit has been opened as above-described,..itV again' closesat` its lcontacts I 2 the energizing ycircuit ofthe relay SR; TherelaySRyupon being thusenergizedffor the third time, is locked up overits contacts 4 5 and over contacts 3 2 -of-now operated relay LO.v

Relay -SR- upon -being energized for the third time" as above .setforth, completes a circuit over its-contacts v2 3 to operate the lampTST and to re-operate therelaySOL This circuit extends from ground-overlcontact `2 of lrelay BY, over contact of relay ST,` over conductor overcontacts A2 3` ofrelay SR to point l0, and thence in parallel.throughthelamp TSTto battery,` `and over Vcontacts Y.8b lb of`deenergizedrelay T1 through thewindingof relay S01 to battery.` Theoperation ofthe .relay S01;v is without significance at thisy time: butlamp TST is caused to glow-'simultaneously-with the ground lamp GND,inclicatinguto 'the operator that anvabnormal condition ,ofdthefinsulation of the -line is indicated by the. ring-tof-ground `test,lThe circuit remains thuslockedup until released by moving the shoe tothev'next line. So long `as. the shoe remains associated with thelinebeing tested, no further tests will be madebecause the relay SR- islocked The operator, upon recording the-fact `thata fault.was.foundon-the line, :.movesfthe shoe to the-next line, therebyopening the connection to the te'st' circuit over .the sleevecontact s`of the shoefandalso the connection over the ring contact -r ofthe-shoe.The-opening of the sleeve contact connection releases relay ST and inturn opens .theinitia-l energizing circuit of the -relay SR and thelocking:- circuit of the relay T2, thereby-restoring the latter. Theopening of the circuit from the ring-,contact r of the shoe causes therelay T3 to release, thereby opening the circuits ofthe ground lamp GND,of the buzzer relay BZ, and of the relay LO. The latter, in falling off,unlocks the relay SR, which, upon being released, opens at its contacts2 3 the energizingcircuit for the test lamp TST andthe relay S01;Thetesting circuit is now in normal conditi-on.

(c) Testing leakage resistance from tip to ring of the Zine Let usassume now that the test circuit, after having made the tip-.to-groundtest Without lindinga line fault, and having thereafter operated therelay T2 to `make the ring-to-gr-o-und test, nds the ring-to-groundleakage resistance above normal. As a consequence, the relay Ts will notbe energized when the testcircuit fromthe ring contact r to groundovercontacts of the relay T2 is completed, as. previously described. Theresult is that the circuits of the ground lamp GND, the buzzerrelay BZand the relay LO are not completed in theY manner previously described.Consequently,` the circuit of the relay SR will not be locked up when itis operated for the third time by the release of relay` SO2 in the`manner above described.

Upon the third operation of relay SR it closes a circuit previouslydescribed over its contacts 2 3 to operate lamp TST and relay S01. RelayS01 at its contacts 2 .opens the circuit of relay SR, Which after aslight delay,V releases. When the relay SR is thus-released upon theoperation of the relay S01, a momentary circuit is vclosedover lcontactsI Vand 2 -of the relay SRto operate the. relay T1, the said circuitextending from ground` overcontact 2 of .relay BY, over contact l ofrelay ST, over conductor x, contacts 2 l of relay SR,lcontacts 3 4 ofVrelay S01, and through the lower winding of relay T1 to battery. RelayT1 `now l operates 1 andv locks up through its upper Winding overV itscontacts H Zt, over yconductorl y, over contacts 6 1 of relay SO2 (whichis released Aat this time), through the windingof relay T1', overcontacts 4t. 3t 2t of relay T2, andthence to ground over contact i ofrelay. ST and contact 2 of .relay BY. Relay T2 remainslocked up at thistime over its contacts Sit- 2L aspreviously described.V Consequently,both relays .T1 and T2 arenow locked up. The relay T1' is also operatedover the locking `path of the relay. vT1 as. above described, and uponclosing4 its .Contact l, bothrelays T1 and T1" are locked .up over .acircuit from battery through the upper 'winding of the relay T1, overcontacts, H Zt ofsaid. relay, over contactl of relay, T1', throughthelwinding of relay T1', and thence ,over a circuitpreviously tracedthrough contacts dii-t-Zt of relay T2 to ground.

Relay T1 upon being operated, prepares a path over its contacts Blf-6bto operate the relay SO2 for the second time: and ybyopening itscontacts 8h lb,lrelay T1' opens the previously described circuit ofthefrelaySO1.; RelaySO1upon releasing,Y again closes theoperating-,circuit of the.

relay SRl over.contacts'2-I "of Vrelay S01.V Re.-

lay SR, upon being thus energized for the fourth time, closes a circuitto operate the lamp TST in parallel with the relay SO2, said circuitextendl ing over a path previously traced from ground over the contactof relay BY, over conductor :c and over contacts 2-3 of relay SR topoint I0. From this point the circuit extends in parallel through thelamp TST to battery and over contacts S17- 6b of relay T1 through thewinding of relay SO2 to battery.

The lamp TST, therefore, glows for the fourth time to indicate to theoperator that the tip-toring testis being made in a manner to bedescribed later. The relay SO2, upon being operated, closes at itscontacts 2-3 a locking circuit from the relay SR from battery throughthe Winding of said relay, over contacts 2--l of relay SO1, overcontacts 2,-3 of relay SO2, over contacts lb-8b of locked up relay T2,over contacts It-Zt of now operated and locked up relay T1, over contactl of relay T1', through the winding of relay Ti', over contacts At-St-Ztof relay T2, over contact l of relay ST, and over contact 2 of relay BYto ground. This locking circuit is independent of the relay LO and henceholds the relay SR locked up with the lamp TST glowing regardless ofwhether the tip-to-ring test detects a fault or not.

We now have a condition under which both relays T1 and T2 have beenenergized and locked up. Under these conditions, a test circuitinvolving the tip and ring conductors of the line can be traced from thetip contact t of the shoe over conductor t', over contacts lb-b of relayT1, over contacts 3b-2b of said relay T1, over conductor n, overcontacts Sla- 5b of relay T2, through the upper winding of relay T3,through battery B, through the middle winding of relay T3, over contactsZIJ-3b of relay T2, and thence over conductor 1" to the ring contact 1'of the test shoe.

If, however, the leakage resistance of the line between ring and sleeveis below normal, the relay T3 will be operated to close its contacts9-'l. This extends a ground connection over said contacts, over contacts81E- St of relay T2, over conductor w, over contacts llt-5t of relay T1,and thence through the shunt lamp SHT and the buzzer relay BZ tobattery. Under these conditions, the buzzer relay BZ operates and theshunt lamp SHT glows simultaneously with the test lamp TST, indicatingthat a fault has been found.

The operation of the relay T3 also closes the circuit for the relay LOfrom ground over contacts 9-4 of relay T3, over contacts B15- Qt ofrelay T2, over conductor w, over contacts lt-5t of relay T1, overconductor u, over contacts 'it-5t of relay T2, over conductor p, overcontacts 'lt--St of relay T1, and thence through the winding of therelay LO to battery. The relay LO is thereby operated, but its operationat this time is without significance because a locking circuit for therelay SR already exists over a circuit previously traced via contacts2-3 of relay SO2.

The operator, having noted the fault indicated by the simultaneousglowing of the lamps TST and SI-IT, moves the test shoe to the nextline, thereby opening the connections established from the sleevecontact s to the relay ST, and from the tip contact t through thewinding of the relay Ts to the ring contact 1. The relay ST is thereforereleased and opens the locking circuits of relays f T2, T1', T1 and SR.The relay SR, in falling oli, opens the circuits previously traced forthe lamp TST and the relay SO2, which are restored.

10 to normal. The relay T3, uponvbeing released, opens the test circuitpreviously traced and also opens the circuit of the relay LO. The buzzerrelay BZ and relay LO now fall off, and the entire circuit is restoredtonormal.

If the tip-to-ring leakage resistance of the line is above the requiredminimum, the relay T3 is not operated by the above circuit, and thecircuit remains in the condition above described with the test lamp TSTglowing alone. This indicates to the operator that the test has beencompleted and that no fault has been found on any one of the three testsmade and he moves the test shoe SH to theY next line to be tested.

While this invention has been disclosed in certain specificarrangementswhich are deemed desirable, it will be obvious that thegeneralprinciples herein set forth maybe embodied in many otherorganizations, widely diierent from those illustrated, without departingfrom the spirit of the invention as defined in the appended claims.

What is claimed is:

1. In a test circuit for ascertaining abnormalleakage conditions on aline, means to make tipto-ground, ring-to-ground, and tip-to-ringleakage resistance tests in a predetermined successive order, said meansincluding an abnormal leakage detector, two test relays, one whenoperated alone associating said detector with a test connection from thetip of a line being tested to ground, the other When operated aloneassociating said detector with a, test connection from the ring of saidline to ground, and means whereby when both relays are operated, saiddetector is associated with a test connection from' the tip to the ringof said line. l c l 2. In a test circuit for ascertaining abnormalleakageconditions on a line, means to make tipto-ground, ring-to-ground,and tip-to-ring leakage resistance tests in a predetermined successiveorder, said means including an abnormal leakage detector, two testrelays, one when operated alone associating said detector with a testconnection from the tip of a line 'being tested to ground, the otherwhen operated alone associating said detector with a test connectionfrom the ring of said line to ground, means whereby when both relays areoperated said detector is associated with a test connection from the tipto the ring of said line, and means acting at diierent times to operateeach of said relays alone, and at another time to operate both relayssimultaneously.

3. In a test circuit for ascertaining abnormal leakage conditions on aline, means to make tipto-ground, ring-to-ground, and tip-to-ringleakage resistance tests in a predetermined successive order, said meansincluding an abnormal leakage detector, two test relays, one whenoperated alone associating said detector with a test connection from thetip of a line being tested to ground, the other when operated aloneassociating said detector with a test connection from the ring of saidline to ground, means whereby when both relays are operated saiddetector is associated with a test connection from the tip to the ringof said line, and means acting at different times to operate each ofsaid relays alone for equal intervals and to operate both relayssimultaneously f or an interval of the same length.

4. In a test circuit for ascertaining abnormal leakage conditions on aline, means to make tipto-ground, ring-to-ground, and tip-to-ri'ngleakage resistance tests in a predetermined successive order, said meansincluding an abnormal leakage detector, two test relays, one whenoperated alone associating said detectorzwth a-test 'connection fromV'the tip of a line'being tested togroundi the o-ther when voperatedalone associatingy said detector with a test connection from the ring ofsaid line to ground; means wherebyl when lboth relaysV are operated`saiddetector is associated with atest connection from the tip yto thering of said line, means actingat diierent `times to operate each ofsaid relays alone for equal intervalsand to operate both-relayssimultaneously yforaninterval'of the same-length, a signal responsivewhen an abnormal leakage-is detected with only one of said relaysoperated and another signal responsive Whent abnormal leakage "isde-"tected with both relays operated.

"5; In-a test circuitsfor:ascertaining abnormal leakagev condi-tionsy ona line, imeans tomake'tip- :to-ground, ring-toground;iand tip-to-:ringleakage 4resistance `tests in-a predetermined successive order, saidmeans includingan abnormal leakaget detector, two test relays,i;one.when operated alone associating said detector With attest :connectionfrom' the tip of a linebeingtestedfto ground, 'the other when operated:alone/.associating saididetector with a test connection-from the .ringof saidv .f yline to ground, meansvwherebyzwhen both relays are operatedsaid` detector :is :associated with a test'connection fromr the tip tothering of said linefand a"controlling"relay-operating at suc- 1 cessiveintervals "When the test vcircuit /is asso- A ciatedwith'an 'idle lineto cause in a 'predeter- 'mined ordenoperationspf each of said relaysalone' and' ofA bothv 'relays simultaneously.

`6.- In ai test circuit forascertaining vabnormal leakage conditions ona line, means to maketip- 1z0-ground, ring-to-ground, and tip-towingleakage resistance :'itests'in: a predetermined succes- --sivexlordensaid ymeans 1inc1uding'an abnormal --'le`akage detectontwovtestrelays;one-When operated alone-associating said'detector Wtha test connectionfrom the tip of a liner being testedA to ground, the other when operatedalone lassociating Vsaid detector with a test connection from the ringof said line to ground, means whereby when both relays are operated saiddetector is associated with a test connection from the 'tip to the ringof ysaid line, andv a controlling relay operating at successive equaltimed intervals When-the test circuit is associated Withan idleline tocause in a predeterminedorder operations ofi each-fof said relays aloneandcf Kboth relays simultane-l ously. Y

"7. In aitest .circuit for ascertaining abnormal leakage conditions onla.line,: means to make tipvto-ground, ringf-to-ground;` and tip-to-ringyleakage resistance. tests in afpredetermined successive:crderfsaidmeans includingYV an abnormal leakage detector; two-.testrelays, konewlien operated alone. associating saidl detector with. a:test

connection from :the tip of. a.line.being 'tested to ground, the.otherrwhen operated `aloney associatring said detectorwith a testconnection fromthe jring of said lineto ground,.means Wherebywhenbothrelays are operated. saiddete'ctor iszassociated with a testconnection fromV the tip to the

